Tuberculosis (TB), which in humans is caused by Mycobacterium tuberculosis, is one of the leading causes of death from infectious diseases worldwide. There are more TB cases now than at any other time in history and this is largely attributed to the HIV epidemic. Factors that make it difficult to thwart the TB epidemic include the lack of an effective vaccine and the requirement for long multidrug treatment regimens to obtain cures. The latter has led to the selection and spread of extensively drug resistance strains that make TB the lethal disease it was in the pre-antibiotic era. TB results from complex interactions between mycobacteria and their vertebrate hosts. Upon infection by pathogenic mycobacteria, macrophages are recruited to the infection site where they phagocytose the bacteria. However, instead of eradicating the bacteria, macrophages migrate into deeper tissues serving to disseminate the infection. Additional uninfected macrophages are then recruited, and aggregate into the hallmark pathological structure of TB, the granuloma. Long thought to be a host beneficial structure that walls off the infection, we have found that the granuloma, at least in its early stages, serves as a vehicle for bacterial expansion and dissemination. To understand the process of granuloma development, we study Mycobacterium marinum, a close genetic relative of M. tuberculosis, in its natural host, the zebrafish. Zebrafish are genetically tractabl vertebrates with a similar complex immune system to that of mammals and are transparent in the early weeks of development. These features allow a detailed, serial, live-monitoring of infection in animals that have been genetically manipulated. The long term objective of this proposal is to better understand the host-pathogen interactions that occur during granuloma development, with the goal of identifying targets for potential host-directed therapeutics. In this proposal specifically, we will use a variety of molecular and genetic techniques to probe pathways of cell death and recruitment during granuloma development, and to identify pharmacological agents that intercept this process to the benefit of the host.